Treating the Treatment Plant

Optimizing energy recovery for the Sunnyvale, California, Water Pollution Control Plant is the task civil engineering students Stephanie Mow, Alison Nojima and Jessica Song took on for their Senior Design project.

While anaerobic digesters at the plant were already producing methane gas to offset the facility’s energy consumption, the team researched ways to increase output through digestion of fats, oils, and greases (FOG) obtained from local restaurants. “We’re considering a system where grease haulers would deliver FOG to a new receiving station at the plant in the early morning hours instead of taking their load to the landfills or other disposal locations. The material will slowly be fed to the digesters during the day, creating methane gas which is captured and converted to energy. Any excess energy can be sold as credits,” said Nojima.

While all three students are civil engineers, their interests within the field vary. Mow focused on sustainability and marketability, researching the economics and environmental benefits to calculate costs, determine savings in landfill emissions, and estimate anticipated kilowatt hours of energy production. Song, with her focus on structural engineering, investigated options for changing the fixed cover on the digesters to a flexible membrane to better manage the variability in gas pressure. For her part, Nojima, as an environmental engineer, designed the receiving station and mixing system and evaluated the additional capacity that could be treated by the digesters.

“I wanted to do something sustainable for my senior project,” said Mow, “and this project just helps the environment in so many ways while also having an economic benefit for the plant. Besides selling energy credits, they can also receive a tipping fee of about five cents per gallon for accepting the waste.” Nojima agreed, “It’s rewarding to take something that is considered waste and turn it into something so valuable.”